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the result by 2—and thus the data portion of the ATM cell contains 48 bytes.

Figure 8.1: The ATM cell.

The fixed size of the ATM cells provides some the following benefits:

∙Efficient bandwidth use of the physical medium

∙Ability of applications to share the network more fairly

∙Accommodation for bursty applications

∙Effective recovery of data loss on the physical wire

Note ATM is based on the switching and multiplexing techniques proposed by the ITU for Broadband Integrated Services Digital Network (BISDN) access.

Time Division Multiplexing

ATM uses a switching and multiplexing method called Time Division Multiplexing (TDM). This method places voice, multimedia, and data into fixed−length cells. These cells are then routed to their destination without regard to content.

TDM combines the information from different resources onto a single serial trunk link that dedicates a predefined timeslot on the multiplexed line for a piece of each resource’s data, as shown in Figure 8.2. If a source has nothing to send, then the timeslot goes unused, and the bandwidth is considered wasted.

Figure 8.2: Data from multiple switch ports (resources) is sent down a single multiplexed serial link.

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